The scanning backlight technique refers to such a technique that in a frame of picture, respective areas of a backlight are turned on in order according to responding timings of liquid crystals, thus enhancing the quality of picture. This technique helps to improve the dynamic quality of picture and contrast of liquid-crystal televisions, and the quality of picture of active-shutter 3D televisions.
In an active-shutter 3D television, a liquid-crystal screen is refreshed alternately with image data of the left and right eye's field of view. When displaying images for the right eye on the screen, the right lens of glasses is opened and the left one closed, and when displaying images for the left eye on the screen, the right lens of glasses is closed and the left one opened. With this cyclic operation, 3D pictures are created through alternating fields of view.
As illustrated in FIGS. 1 and 2, four areas shown as A, B, C and D are areas which respond to liquid-crystal screen image signals. When area A finishes responding, LEDs of area A are turned on, and then followed in turn by areas B, C and D. Within the time of one single frame, the four areas A, B, C and D turn on and off the respective LEDs once, and since the time during which the 3D glasses is opened within that frame concentrates primarily on the period of time during which the LEDs of the two areas B and C are turned on, more light is received from areas B and C through the 3D glasses. On the other hand, the 3D glasses is opened only for a small fraction of time while the two areas A and D are turned on, therefore less light is received through the 3D glasses, thus making the two areas A and D appear darker than the two areas B and C for people wearing the glasses. As shown in FIG. 2, four waveforms in the middle are timings corresponding to the four areas A, B, C and D, respectively, and the waveform at the bottom of FIG. 2 is a timing diagram of the 3D glasses. In 3D mode, since an opening time of the 3D glasses is limited, an integral value of brightness over the time while the 3D glasses is opened represents the brightness of the respective area, i.e., the area of the shadowed portion in FIG. 2 represents the brightness under the 3D glasses, and apparently, areas A and D are darker than areas B and C. That is to say, a situation could occur that the brightness of picture is uneven when the same frame of picture is being viewed, and the picture goes darker towards the two edges, thus offering poor viewing effects.